Stabilized phenolic resole resin compositions and their use

ABSTRACT

This invention relates to a stabilized phenolic resole resin composition comprising a phenolic resole resin and an effective stabilizing amount of an ortho ester. The invention also relates to phenolic urethane binders prepared with the phenolic resole resin compositions, and the use of the binders to make foundry mixes, foundry shapes, and metal castings.

TECHNICAL FIELD OF THE INVENTION

This invention relates to a stabilized phenolic resole resin composition comprising a phenolic resole resin and an effective stabilizing amount of an ortho ester. The invention also relates to phenolic urethane binders prepared with the phenolic resole resin compositions, and the use of the binders to make foundry mixes, foundry shapes, and metal castings.

BACKGROUND OF THE INVENTION

One of the major processes used in the foundry industry for making metal parts is sand casting. In sand casting, disposable foundry shapes (usually characterized as molds and cores) are made by shaping and curing a foundry binder system that is a mixture of sand and an organic or inorganic binder. The binder is used to strengthen the molds and cores.

Two of the major processes used in sand casting for making molds and cores are the no-bake process and the cold-box process. In the no-bake process, a liquid curing agent is mixed with an aggregate and shaped to produce a cured mold and/or core. In the cold-box process, a gaseous curing agent is passed through a compacted shaped mix to produce a cured mold and/or core. Phenolic urethane binder, cured with a gaseous tertiary amine catalyst, are often used in the cold-box process to hold shaped foundry aggregate together as a mold or core. See for example U.S. Pat. No. 3,409,579. The phenolic urethane binder system usually consists of a phenolic resin component and polyisocyanate component, which are mixed with sand prior to compacting and curing to form a foundry binder system.

Among other things, the binder must have a low viscosity, be gel-free, remain stable under use conditions, and cure efficiently. The foundry binder system made by mixing sand with the binder must have adequate benchlife or the mix will not shape and cure properly. The cores and molds made with the binders must have adequate tensile strengths under normal and humid conditions, and release effectively from the pattern. Binders that meet all of these requirements are not easy to develop.

One of the problems with the phenolic resole resins used in phenolic urethane binders is that they are heat sensitive, and thus are not stable when stored at or exposed to elevated temperature for a prolonged period of time. This causes the viscosity of the resin to increase, or in extreme cases, the resin will gel. This seriously adversely affects the quality and performance of the binder.

Ortho esters are known in the prior art to stabilize organic isocyanates. U.S. Pat. No. 3,535,359 (Chadwick) discloses that certain ortho-esters are capable of stabilizing a polyisocyanate against several different kinds of degradation, for instance moisture, and viscosity increases, even when only small amounts of ortho esters are used. The stabilized isocyanates are useful in the preparation of polyurethane foam, nonporous plastics including polyurethane castings such as gear wheels and the like, and coating compositions. Chadwick does not disclose the use of such polyisocyanates in foundry binders, foundry mixes, or the preparation of foundry shapes and metal castings.

U.S. Pat. No 6,288,139 discloses phenolic urethane binders wherein the polyisocyanate component contains an ortho ester. The patent indicates that, when added to a polyisocyanate component that contains a non reactive organic solvent, the ortho ester improves the tensile strength of foundry shapes. It also indicates that polyisocyanate components containing the ortho ester have lower turbidity, which indicates that it is more stable or homogeneous. As a result the polyisocyanate component will not be subjected to settling of particulate matter, and will be easier to pump. This patent does not teach or suggest the use of ortho esters in the phenolic resole resin component of the phenolic urethane binder.

SUMMARY OF THE INVENTION

This invention relates to stabilized phenolic resole resin compositions comprising a phenolic resole resin and an effective stabilizing amount of an ortho ester. The invention also relates to phenolic urethane binders prepared with the phenolic resole resin compositions, and the use of the binders to make foundry mixes, foundry shapes, and metal castings.

The addition of the ortho ester was found to be an effective stabilizing agent to improve the shelf stability of the phenolic resole resin composition. The advantages of using the ortho ester in the phenolic resole resin composition are:

-   -   (1) the phenolic resole resin composition has better shelf         storage stability if it contains the ortho ester, and     -   (2) the phenolic resole resin composition has improved heat         stability at elevated temperatures if it contains the ortho         ester.

Shelf stability and heat stability are demonstrated because the phenolic resole resin composition does not undergo viscosity increase or gelation, even when subjected to increased temperatures. This advantage is particular important when the phenolic resole resin composition is stored and exposed at elevated temperatures during summer time.

DETAILED DESCRIPTION OF THE INVENTION

The phenolic resole resin used in the phenolic resole resin composition is preferably prepared by reacting an excess of aldehyde with a phenol in the presence of either an alkaline catalyst or a metal catalyst. The phenolic resins are preferably substantially free of water and are organic solvent soluble. The preferred phenolic resins used in the subject binder compositions are well known in the art, and are specifically described in U.S. Pat. No 3,485,797, which is hereby incorporated by reference. These resins, known as benzylic ether phenolic resole resins, are the reaction products of an aldehyde with a phenol. They contain a preponderance of bridges joining the phenolic nuclei of the polymer, which are ortho-ortho benzylic ether bridges. They are prepared by reacting an aldehyde and a phenol in a mole ratio of aldehyde to phenol of at least 1:1 in the presence of a metal ion catalyst, preferably a divalent metal ion such as zinc, lead, manganese, copper, tin, magnesium, cobalt, calcium, and barium.

Alkoxy-modified benzylic ether phenolic resole resins can also be used. The resins are prepared by reacting an excess of aldehyde with a phenol and an alcohol in the presence of a metal ion catalyst according to methods well known in the art. Alternatively, they can be prepared by preparing a benzylic ether phenolic resole resin and post-capping with the alcohol. See, for example, U.S. Pat. No 4,546,124 for a discussion of how these resins are prepared.

The phenols use to prepare the phenolic resole resins include any one or more of the phenols which have heretofore been employed in the formation of phenolic resins and which are not substituted at either the two ortho-positions or at one ortho-position and the para-position. These unsubstituted positions are necessary for the polymerization reaction. Any of the remaining carbon atoms of the phenol ring can be substituted. The nature of the substituent can vary widely and it is only necessary that the substituent not interfere in the polymerization of the aldehyde with the phenol at the ortho-position and/or para-position. Substituted phenols employed in the formation of the phenolic resins include alkyl-substituted phenols, aryl-substituted phenols, cyclo-alkyl-substituted phenols, aryloxy-substituted phenols, and halogen-substituted phenols, the foregoing substituents containing from 1 to 26 carbon atoms and preferably from 1 to 12 carbon atoms.

Specific examples of suitable phenols include phenol, 2,6-xylenol, o-cresol, p-cresol, 3,5-xylenol, 3,4-xylenol, 2,3,4-trimethyl phenol, 3-ethyl phenol, 3,5-diethyl phenol, p-butyl phenol, 3,5-dibutyl phenol, p-amyl phenol, p-cyclohexyl phenol, p-octyl phenol, 3,5-dicyclohexyl phenol, p-phenyl phenol, p-crotyl phenol, 3,5-dimethoxy phenol, 3,4,5-trimethoxy phenol, p-ethoxy phenol, p-butoxy phenol, 3-methyl-4-methoxy phenol, and p-phenoxy phenol. Multiple ring phenols such as bisphenol A and bisphenol F are also suitable.

The aldehyde used to react with the phenol has the formula RCHO wherein R is a hydrogen or hydrocarbon radical of 1 to 8 carbon atoms. The aldehydes reacted with the phenol can include any of the aldehydes heretofore employed in the formation of phenolic resins such as formaldehyde, acetaldehyde, propionaldehyde, furfuraldehyde, and benzaldehyde. The most preferred aldehyde is formaldehyde.

The phenolic resin used must be liquid or organic solvent-soluble. The phenolic resin composition generally contains an organic solvent. The amount of solvent used should be sufficient to result in a binder composition permitting uniform coating thereof on the aggregate and uniform reaction of the mixture. The specific solvent concentration for the phenolic resin composition will vary depending on the type of phenolic resin employed and its molecular weight. In general, the solvent concentration will be in the range of up to 80% by weight of the resin solution and preferably in the range of 20% to 80%.

As was mentioned previously, the phenolic resole resin composition contains an ortho ester. The ortho esters used have the formula R′C(OR)₃, where R′ is hydrogen, alkyl, alkenyl, aryl, haloalkyl and R is alky or alkenyl of 1 to 18 carbon atoms, chloroethyl, or phenyl. The ortho esters are disclosed in U.S. Pat. No 3,535,359, which is incorporated by reference into this specification. Preferably used are triethyl orthoformate, trimethyl orthoformate, and mixtures thereof. The amount of ortho ester used is from 0.1 to 5.0 weight percent based upon the weight of the phenolic resole resin, preferably from 0.1 to 1.5 weight percent, most preferably from 0.1 to 0.4 weight percent

The phenolic resole resin compositions are used in the phenolic urethane binders. These binders contain a phenolic resin component and a polyisocyanate component, and are typically cured with a tertiary amine curing catalyst.

The polyisocyanate component of the binder typically comprises a polyisocyanate and organic solvent. The polyisocyanate has a functionality of two or more, preferably 2 to 5. It may be aliphatic, cycloaliphatic, aromatic, or a hybrid polyisocyanate. Mixtures of such polyisocyanates may be used. Also, it is contemplated that capped polyisocyanates, prepolymers of polyisocyanates, and quasi prepolymers of polyisocyanates can be used. Optional ingredients such as release agents may also be used in the polyisocyanate hardener component.

Representative examples of polyisocyanates which can be used are aliphatic polyisocyanates such as hexamethylene diisocyanate, alicyclic polyisocyanates such as 4,4′-dicyclohexylmethane diisocyanate, and aromatic polyisocyanates such as 2,4-, 2,4-, 2,6-toluene diisocyanate and 2,2′-, 2,4′-, 4,4′-diphenylmethane diisocyanate, and dimethyl derivates thereof. Other examples of suitable polyisocyanates are 1,5-naphthalene diisocyanate, triphenylmethane triisocyanate, xylylene diisocyanate, and the methyl derivates thereof, polymethylenepolyphenyl isocyanates, chlorophenylene-2,4-diisocyanate, and the like.

The polyisocyanates are used in sufficient concentrations to cause the curing of the phenolic resin in the presence of the curing catalyst. In general the polyisocyanate ratio of the polyisocyanate to the hydroxyl of the phenolic resin is from 1.25:1 to 1:1.25, preferably about 1:1. Expressed as weight percent, the amount of polyisocyanate used is from 10 to 500 weight percent, preferably 20 to 300 weight percent, based on the weight of the phenolic resin.

The polyisocyanate is used in a liquid form. Solid or viscous polyisocyanate must be used in the form of organic solvent solutions. In general, the solvent concentration will be in the range of up to 80% by weight of the resin solution and preferably in the range of 20% to 80%.

Those skilled in the art will know how to select specific solvents for the phenolic resin component, and in particular the solvents required in the polyisocyanate component. It is known that the difference in the polarity between the polyisocyanate and the phenolic resins restricts the choice of solvents in which both components are compatible. Such compatibility is necessary to achieve complete reaction and curing of the binder compositions of the present invention. Polar solvents of either the protic or aprotic type are good solvents for the phenolic resin, but have limited compatibility with the polyisocyanate. Aromatic solvents, although compatible with the polyisocyanate, are less compatible with the phenolic results. It is, therefore, preferred to employ combinations of solvents and particularly combinations of aromatic and polar solvents.

Examples of aromatic solvents include xylene and ethylbenzene. The aromatic solvents are preferably a mixture of aromatic solvents that have a boiling point range of 125° C. to 250° C. The polar solvents should not be extremely polar such as to become incompatible with the aromatic solvent. Suitable polar solvents are generally those which have been classified in the art as coupling solvents and include furfural, furfuryl alcohol, cellosolve acetate, butyl cellosolve, butyl carbitol, diacetone alcohol, and “Texanol”.

The binder may also contain a silane (typically added to the phenolic resin component) having the following general formula:

wherein R′ is a hydrocarbon radical and preferably an alkyl radical of 1 to 6 carbon atoms and R is an alkyl radical, an alkoxy-substituted alkyl radical, or an alkyl-amine-substituted alkyl radical in which the alkyl groups have from 1 to 6 carbon atoms. The silane is preferably added to the phenolic resin component in amounts of 0.01 to 2 weight percent, preferably 0.1 to 0.5 weight percent based on the weight of the phenolic resin component.

When preparing an ordinary sand-type foundry shape, the aggregate employed has a particle size large enough to provide sufficient porosity in the foundry shape to permit escape of volatiles from the shape during the casting operation. The term “ordinary sand-type foundry shapes,” as used herein, refers to foundry shapes which have sufficient porosity to permit escape of volatiles from it during the casting operation.

The preferred aggregate employed for preparing ordinary foundry shapes is silica wherein at least about 70 weight percent and preferably at least about 85 weight percent of the sand is silica. Other suitable aggregate materials include zircon, olivine, aluminosilicate,=Remove Comma sand, chromite sand, and the like. Although the aggregate employed is preferably dry, it can contain minor amounts of moisture.

In molding compositions, the aggregate constitutes the major constituent and the binder constitutes a relatively minor amount. In ordinary sand type foundry applications, the amount of binder is generally no greater than about 10% by weight and frequently within the range of about 0.5% to about 7% by weight based upon the weight of the aggregate. Most often, the binder content ranges from about 0.6% to about 5% by weight based upon the weight of the aggregate in ordinary sand-type foundry shapes.

The binder compositions are preferably made available as a two-package system with the phenolic resin component in one package and the polyisocyanate component in the other package. Usually, the phenolic resin component is first mixed with sand and then the polyisocyanate component is added. Methods of distributing the binder on the aggregate particles are well known to those skilled in the art.

The foundry binder system is molded into the desired shape, such as a mold or core, and cured. Curing by the cold-box process is carried out by passing a volatile tertiary amine, preferably triethyl amine, through the shaped mix as described in U.S. Pat. No 3,409,579. Curing by the no-bake process takes place by mixing a liquid amine curing catalyst into the foundry binder system, shaping it, and allowing it to cure.

Useful liquid amines have a pK_(b) value generally in the range of about 7 to about 11. Specific examples of such amines include 4-alkyl pyridines, isoquinoline, arylpyridines, 1-methylbenzimidazole, and 1,4-thiazine. Preferably used as the liquid tertiary amine catalyst is an aliphatic tertiary amine, particularly tris (3-dimethylamino) propylamine. In general, the concentration of the liquid amine catalyst will range from about 0.2 to about 5.0 percent by weight of the phenolic resin, preferably 1.0 percent by weight to 4.0 percent by weight, most preferably 2.0 percent by weight to 3.5 percent by weight based upon the weight of the phenolic resin.

EXAMPLES

While the invention has been described with reference to a preferred embodiment, those skilled in the art will understand that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims. In this application, all amounts and percentages are by weight, unless otherwise expressly indicated. The following abbreviations are used in the examples:

-   -   TMOF trimethyl ortho-formate.     -   PEP SET® 1670/2670 a phenolic urethane no-bake foundry binder,         manufactured by Ashland Specialty Chemical Company. PEP SET 1670         is the phenolic component and comprises about 50-60 weight         percent PR, 20-30 weight percent aromatic solvent, and 10-20         weight percent ester solvent. PEP SET 2670 is the isocyanate         component and comprises about 60-80 weight percent isocyanate,         and 30-40 weight percent aromatic solvents.     -   PR a polybenzylic ether phenolic resin prepared with zinc         acetate dihydrate as the catalyst and modified with the addition         of 0.09 mole of methanol per mole of phenol prepared along the         lines described in the examples of U.S. Pat. No 3,485,797.     -   Wedron 540 sand silica sand commonly used in the foundry         industry.     -   RH relative humidity.     -   ST striptime is the time interval for a foundry mix to reach a         green hardness of 90.     -   WT worktime is the time interval for a foundry mix to reach a         green hardness of 60.

The following examples demonstrate the use of TMOF in phenolic urethane no-bake foundry binder applications.

Examples A, 1, and 2 (Heat Stability Tests of Phenolic Resins)

In order to test the heat stability of the phenolic resin compositions with and without TMOF, 200 grams of PEP SET 1670 binder were placed in 8-oz plastic bottles. The samples were stored at 60° C. for 80 days. The viscosity of the samples was measured after 1 day and after 80 days by using Brookfield viscosity cone and plate viscosity method. The results are summarized in Table I. TABLE I (Effect of TMOF on the Heat Stability of Phenolic Component) (Samples stored at 60° C. for 80 days) Phenolic Viscosity (cp) component TMOF¹ Day 1 Day 80 Control A² 0.0 165 >1,000,000, partially gelled Example 1 0.7 163 2,640 Example 2 1.4 162 862 ¹Weight percent based upon the weight of the phenolic resin component. ²PEP SET ® 1670 phenolic resin component

Table I shows that the incorporation of TMOF as stabilizing agent at levels of 0.7 and 1.4% by weight into the phenolic component (PEP SET 1670) greatly improved the shelf storage stability of the phenolic component at 60° C. The control sample (A) gelled out, while Example 1 and 2 were pourable liquids after 80 days storage at 60° C. Table I also indicates that the higher level of TMOF used, the greater the heat stability of the phenolic resole resin component. This is particular important during the hot summer time, where the temperature can reach 50° C. during the shipping and handling of the foundry binder.

Examples B, 3, and 4 (Effect of Using TMOF on Strength of Cores Made with Binder)

Test cores were made with PEP SETS® 1670/2670 using Wedron 540 sand at a binder level of 1.2%, based upon the weight of the sand, a Part I/Part II mix ratio of 55/45 mix ratio, and PEP SET 3502 catalyst (4-phenyl propyl pyridine in an aromatic solvent) in an amount of about 3 weight percent based upon the Part I.

Tensile strengths of test dog bone shapes were measured according to the AFS standard tensile strength test. Determining the tensile strengths of the dog bone test shapes enables one to predict how the mixture of sand and binder will work in actual foundry facilities. The dog bones were stored for 1.0 hour, 3 hours and 24 hours in a constant temperature room at relative humidity of 50% and a temperature of 25° C. before measuring their tensile strengths. Unless otherwise specified, the tensile strengths were also measured on dog bone specimens stored 24 hours at a relative humidity (RH) of 90%. The results of these tests are shown in Table II. TABLE II (Effect of TMOF on sand tensile performance) WT/ST 1 Hr 3 Hrs 24 Hrs 24 Hr Binder TMOF level³ (min)

[psi]

@ 90% RH Control B 0.0 3.0/4.0 152 166 200 70 Example 3 0.7 3.8/4.2 159 181 212 65 Example 4 1.4 3.5/4.2 136 192 185 63 ³Weight percent based upon the weight of the phenolic resin component

The data indicate that addition of TMOF to the phenolic resole resin component has little effect on the sand tensile strength development. The data in Tables I and II indicate that adding TMOF into the phenolic resin component, while increasing the heat stability of the phenolic resin component, does not adversely effect the desired core-making properties.

Examples C, 5, and 6 (Heat Stability Tests of Phenolic Resins Where Zinc Catalyst Was Removed)

The procedure of Examples A, 1, and 2 was followed, except the zinc catalyst used to make the resin was removed from the resin. The results are summarized in Table III. TABLE III (Effect of TMOF on the Heat Stability of Phenolic Component) (Samples stored at 60° C. for 80 days) Phenolic Viscosity (cp) component TMOF⁴ Day 1 Day 80 Control C 0.0 75 595 Example 5 0.7 74 367 Example 6 1.4 73 319 ⁴Weight percent based upon the weight of the phenolic resin component.

The data in Table III indicate that the phenolic resole resin component without the zinc catalyst had a much lower viscosity to begin with. However, the effect of TMOF on the heat stability of the phenolic component is still evident. The addition of TMOF to the phenolic resin component improved the heat stability of the phenolic resin component, which is shown by the data indicating that there was little change in viscosity in the samples containing the TMOF.

Examples D, 7, and 8 (Effect of Using TMOF on Strength of Cores Made with Binder)

Test cores using the procedure set forth in Examples B, 3, and 4, except the phenolic resin of Examples C, 5, and 6, which had the zinc catalyst removed, was used as the resin. The results of these tests are shown in Table IV. TABLE II (Effect of TMOF on sand tensile performance) WT/ST 1 Hr 3 Hrs 24 Hrs 24 Hr Binder TMOF level⁵ (min)

[psi]

@ 90% RH Control D 0.0 6.5/7.5 157 186 235 102 Example 7 0.7 7.0/8.3 133 183 253 104 Example 8 1.4  8.5/10.2 111 158 206 103 ⁵Weight percent based upon the weight of the phenolic resin component

The data in Table IV indicate that addition of TMOF to the phenolic resole resin component in this case had some adverse affect on the core strength, particularly at the 1.4% level. It is noted that the presence of TMOF slightly increases the work time/strip time of this no-bake binder. However, these adverse affects are not a problem from commercial standpoint, and the advantages that the use of TMOF provides in terms of increased heat stability outweighs these disadvantages. 

1. A stabilized phenolic resole resin composition comprising a phenolic resin and an effective stabilizing amount of an ortho ester.
 2. The stabilized phenolic resole resin composition of claim 1 which also contains a solvent selected from the group consisting of aromatic hydrocarbon solvents, ester solvents, and mixtures thereof.
 3. The stabilized phenolic resole resin composition of claim 2 wherein the stabilized phenolic resole resin composition comprises a polybenzylic ether phenolic resin prepared by reacting an aldehyde with a phenol such that the molar ratio of aldehyde to phenol is from 1.1:1 to 3:1 in the presence of a divalent metal catalyst.
 4. The stabilized phenolic resole resin composition of claim 3 wherein the phenol used to prepare the phenolic resole resin of the stabilized phenolic resole resin composition is selected from the group consisting of phenol, bisphenol, o-cresol, p-cresol, and mixtures thereof.
 5. The stabilized phenolic resole resin composition of claim 4 wherein the aldehyde used to prepare the phenolic resin of the stabilized phenolic resole resin composition is formaldehyde.
 6. The stabilized phenolic resole resin composition of claim 5 wherein the ortho ester is selected from the group consisting of triethyl orthoformate, trimethyl orthoformate, and mixtures thereof.
 7. The stabilized phenolic resole resin composition of claim 6 wherein the amount of solvent in the resin composition is from 20 weight percent to 80 weight percent based upon the weight of the phenolic resin composition.
 8. The stabilized phenolic resole resin composition of claim 7 wherein the amount of ortho ester is from about 0.1 weight percent to about 1.5 weight percent based upon the weight of the phenolic resin.
 9. The stabilized phenolic resole resin composition of claim 6 wherein the phenolic resole resin of the stabilized phenolic resole resin composition is an alkoxy-modified benzylic ether phenolic resole resin and the catalyst used to prepare said resin is a divalent zinc salt.
 10. A foundry binder system comprising the phenolic resole resin component of claim 1, 2, 3, 4, 5, 6, 7, 8, or 9 and a polyisocyanate component.
 11. A foundry mix comprising: A. a major amount of an aggregate; and B. an effective bonding amount of the binder system of claim
 10. 12. A process for preparing a foundry shape which comprises: (a) forming a foundry mix as set forth in claim 10; (b) forming a foundry shape by introducing the foundry mix obtained from step (a) into a pattern; (c) contacting the shaped foundry binder system with a tertiary amine catalyst; and (d) removing the foundry shape of step (c) from the pattern.
 12. The process of claim 11 wherein the tertiary amine catalyst is a gaseous tertiary amine catalyst.
 13. The process of claim 12 wherein the amount of said binder composition is about 0.6 percent to about 5.0 percent based upon the weight of the aggregate.
 14. The process of claim 10 wherein the tertiary amine catalyst is a liquid tertiary amine catalyst.
 15. The process of casting a metal which comprises: (a) preparing a foundry shape in accordance with claim 12; (b) pouring said metal while in the liquid state into and a round said shape; (c) allowing said metal to cool and solidify; and (d) then separating the molded article. 